1,721,224 research outputs found
Role of the deposition parameters and aging on the optical and photoluminescence properties of C70 films
No full textWe have investigated the influence of the growth parameters (substrate temperature and deposition rate) and the aging process on the optical
properties of C70 thin films, by means of absorption and photoluminescence spectra. The Urbach energy, obtained from the absorption spectra,
indicates that the substrate temperature influences the film optical properties more than the deposition rate. The luminescence spectra suggest the
important role of the disorder in the radiative efficiency. The main structures of the emission spectra have been assigned to an intramolecular
polaron–exciton. The analysis of the temperature dependence of the photoluminescence spectra of the as-deposited samples shows that the
vibronic transitions are dominant at low temperature, whereas the singlet purely electronic recombination (due to Frenkel-type exciton) is visible at
a sufficiently high temperature. On the contrary, in the aged samples this purely electronic transition is well resolved from low to high temperature.
This anomalous behaviour is discussed and attributed to the disorder introduced in the film.
© 2007 Elsevier B.V. All rights reserved
Effects of Structural Disorder on the Optical and Vibrational Properties of CdSXSel-X Alloy Thin Films Deposited by Laser Ablation
No full textOptical Spectroscopy and Structural Properties of Synthetic and Natural Eumelanin
Full text linkOptical properties of synthetic and natural eumelanin are presented and compared, in order to investigate the structural organization of eumelanin, which is related to the function of this biopolymer. Synthetic eumelanin is produced by oxidation of tyrosine
with hydrogen peroxide, whereas natural eumelanin is extracted from Sepia Officinalis
and from Rana Esculenta. Vibrational spectroscopy techniques (as Raman scattering and infrared absorption) show that both types of biopolymer include chemical functional groups characteristic of the monomeric units of eumelanin, although natural eumelanin includes also protein-related groups, proportionally to the protein content. X-ray diffraction spectra are in agreement with the hypothesis that eumelanin monomers assembly themselves and form protomolecules consisting of stacked layers (distant 3 – 4 Å each other) of indolic sheets. Absorption measurements, characterized by a monotonic increase of optical density from near-IR to UV range, support the model that eumelanin consists of a distribution of aggregates of oligomeric structures having different size and chemical composition. The estimated values of the optical gap indicate that the natural eumelanins are characterized by a larger structural disorder than the synthetic one. Fluorescence spectra confirm that the biopolymer consists of ensembles of chemically distinct oligomer systems, which can be selectively excited. This result is also supported
by Dynamic Light Scattering measurements, which permit to visualize the distribution of particles size. In fact, the nanoaggregate systems of natural eumelanin have a larger size than those of synthetic eumelanin. This might be related to the biological functions of such a biopolymer, particularly as far as photoprotective action is concerned
Structural and optical properties of II-VI semiconductor thin films deposited by laser ablation
No full textExperimental results on the structural and optical properties of CdSxSe1-x films deposited by pulsed laser ablation technique are reviewed. Technical details of the laser ablation process and deposition apparatus are illustrated. The influence of growth parameters on the physical properties of deposited films is discussed. The more critical growth parameters result to be the energy density of the laser pulse, which is strongly related to the crystalline grain dimensions, and the substrate temperature, which dramatically influences the preferential orientation of the polycrystalline films. The asymmetric lineshape of the LO phonon structure in micro-Raman spectra and the large contribution of the acoustic phonons to the thermal gap shrinkage in absorption and photoluminescence measurements are related to the alloy disorder. The disorder causes also the localization of excitons and a strong enhancement of the radiative efficiency. Band gap narrowing and band tails are observed in the absorption spectra when heavy doping occur
Spettroscopia Raman e microscopia AFM di cheratinociti umani: modificazioni cellulari dopo esposizione a basse dosi di agenti xenobiotici
No full textOggigiorno vengono utilizzati e dispersi nell’ambiente vari prodotti chimici nelle attività agricole, domestiche ed industriali, ma sono poco chiari gli effetti relativi a situazioni di esposizione a basse dosi di alcune di esse. Sebbene gli effetti tossici coinvolgano organi specifici, gli eventi che sono alla base di tali effetti hanno origine da alterazioni a livello cellulare. Pertanto, è interessante valutare a livello cellulare gli effetti conseguenti all’azione di sostanze chimiche a cui la popolazione è esposta.
In questa relazione si presentano alcuni effetti che si manifestano su cheratinociti umani normali esposti a basse dosi di inquinanti ambientali (alcuni pesticidi e HgCl2), valutati mediante microspettroscopia Raman e Microscopia a Forza Atomica (AFM). Variazioni biochimiche e morfologiche sono evidenti in seguito ad esposizione a dosi molto inferiori a quelle citotossiche. Le variazioni biochimiche riguardano legami proteici, basi di DNA e membrane lipidiche. Queste ultime sono anche caratterizzate morfologicamente da un aumento della rugosità. Questi risultati hanno evidenziato la possibilità di utilizzare la microspettroscopia Raman e la microscopia AFM come mezzi diagnostici per una precoce rivelazione di danni cellulari indotti da stress chimico
Preliminary numerical analysis of the Vibro-Impact Isolation systems under seismic excitations
No full textThe problem of large displacements in isolated structures can cause undesirable effects, such as damage to isolation systems or increases in superstructure accelerations. In order to limit these undesirable effects, the authors propose a new integrated design methodology of vibro-impact isolation systems that aims to control large displacements while limiting the increase in accelerations due to the impact phenomenon. Therefore, this paper shows numerical results obtained on single-degree-of-freedom systems isolated at the base subjected to seismic excitations and constrained by two deformable and dissipative devices
Raman spectroscopy of human neuronal and epidermal cells exposed to an insecticide mixture of chlorpyrifos and deltamethrin
No full textMany pesticides are increasingly used in combinations for crop protection. Their chemical stability ensures the presence of such mixtures, both in the workspaces of the operators involved in agricultural activities and in foodstuffs, thus making probable human exposure to such chemicals in the environment. This investigation, performed by means of Raman microspectroscopy and principal component analysis, concerns the effects of in vitro cellular exposure to a commercial insecticide based on a chlorpyrifos and deltamethrin mixture. The investigated cells belong to the SHSY-5Y and human keratinocyte (HUKE) cell lines, which can be considered representative of neuronal and epidermal cells, respectively. After 24 h exposure at a concentration one-tenth of that usually used by operators, about 50% of the investigated cells were dead and the relative content of the biochemical components of both types of cells that were still alive had been affected by the exposure. A statistically significant decrease in the protein and nucleic acid content occurred in the SHSY-5Y cells, and a lowering of the lipid and carbohydrate content was observed in the HUKE cells. This study shows the utility of Raman microspectroscopy and principal component analysis for the investigation of the effects on human cells of environmental exposure to any chemicals
Refecltance and photoluminescence characterization of CdS and CdSe heteroepitaxxial films deposited by laser ablation technique
No full textComparison of FTIR spectra of different breast cell lines to detect spectral biomarkers of pathology
No full textMany efforts have been made for several years to make Fourier Transform Infrared (FTIR) micro-spectroscopy
usable in the cytological diagnostic. In fact, some events arising when cells undergo a disease, as alterations
in the relative content of biochemical cellular components and variations of the proteins secondary structure,
lead to modifications of the FTIR spectra, as changes of relative intensity and/or spectral shifts of specific peaks.
In this study, we compare FTIR spectra measured for three different breast cell lines: the non-malignant MCF10A
cell line, the malignant non-metastatic MCF7 cell line and the metastatic MDA cell line. The major differences of
average absorption spectra involve a blue-shift of amide I and II bands and a larger relative intensity of nucleic
acid bands in MCF7 spectra with respect to the other ones. Curve fitting also provided important information
about spectral markers able to discriminate the three cell lines. In fact, the ratio of sum of the areas of peaks at
2852 and 2922 cm 1 with respect to the sum of the areas of peaks at 2873 and 2958 cm 1 is able to differentiate
the non-malignant, malignant and metastatic cells among them. These results suggest that FTIR microspectroscopy
may be a potentially useful tool for breast cancer diagnosis at cytological level
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